By way of background, reference is made to the prior disclosures of techniques for isotopically selective photoexcitation and ionization of uranium as represented in commonly assigned U. S. Pat. No. 3,772,519, 3,994,947 and Belgian Pat. No. 807.118, and additionally to German patent publication 2,312,194. The techniques there presented include photoexcitation in one or more steps along with photoionization which may be via an autoionization transition. As known in the art, autoionization is a transition which excites particles to an energy level above ionization from which it degenerates into an ion and a released electron. In application to uranium enrichment the suggested utilization of an autoionization transition would have the advantage of increasing the normally low cross-section for ionization, thereby reducing the requirements on the ionization excitation source or laser.
Until the present invention, however, efficient utilization of autoionization in an isotope separation technique has not been identified.